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This invention relates to a vibration damping silicone composition of superior vibration damping properties and storage stability.
Vibration damping silicone compositions containing solid powders and viscous liquids such as silicone oil are known in the art. Some examples are (i) a vibration damping composition containing a silicone oil and a solid powder such as silica powder, glass powder, or silicone resin powder, as described in Japanese Patent Application Publication No. Sho 63(1988)-308241; (ii) a vibration damping silicone composition containing a silicone oil and silicone resin powder as described in Japanese Patent Application Publication No. Hei 10(1998)-251517; and (iii) a vibration damping compound containing a silicone oil, a polyorganosilsesquioxane resin powder, and a calcium carbonate powder as described in Japanese Patent Application Publication No. 2000-080277. However, these compositions typically undergo changes when stored over extended periods of time or used over extended periods of time, and as a result, their vibration damping properties are deteriorated.
Therefore, this invention is directed to vibration damping silicone compositions of superior vibration damping properties and storage stability, based on the discovery that changes in vibration damping properties tend to occur over time, when the content of volatile components in certain silicone resin powders exceeds one percent.
These and other features of the invention will become apparent from a consideration of the detailed description.
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Thus, the present invention relates to vibration damping silicone compositions containing (A) 100 parts by weight of a silicone oil; and (B) 10-300 parts by weight of a silicone resin powder that is a solid at room temperature. Component (B) has a volatile component content of not more than one percent by weight after being heated for two hours at 200xc2x0 C.
Silicone oil component (A) functions as the matrix for dispersing the silicone resin powder component (B). The silicone oil is an organopolysiloxane that is in the liquid state at room temperature. Groups bonded to the silicon atoms in such organopolysiloxane silicone oils are typically monovalent hydrocarbon groups, representative of which are alkyl groups such as methyl, ethyl, and propyl; alkenyl groups such as vinyl, allyl, and butenyl; aryl groups such as phenyl and tolyl. Halogenated alkyl groups such as 3,3,3-trifluoropropyl can also be used. In addition, hydroxyl groups, or alkoxy groups such as methoxy, and ethoxy, can be substituted for some of the foregoing groups. Alkyl groups are preferable, however, particularly the methyl group, because such silicone oil compositions have a very low changes in viscosity based on temperature, and have excellent storage stability.
Component (A) can have a molecular structure which is linear, partially branched linear, branched, or cyclic. A linear structure is preferred. Component (A) should have a kinematic viscosity at 25xc2x0 C. of 100-1,000,000 mm2/s, preferably 500-500,000 mm2/s. When the kinematic viscosity at 25xc2x0 C. is less than 100 mm2/s, it is difficult to maintain component (B) in a uniformly dispersed state in component (A). When it exceeds 1,000,000 mm2/s, handling properties deteriorate, and component (B) becomes difficult to disperse in component (A).
Component (A) can be exemplified by dimethylpolysiloxanes end blocked with trimethylsiloxy groups, methyloctylpolysiloxanes end blocked with trimethylsiloxy groups, dimethylpolysiloxanes end blocked with silanol groups, and copolymers of methylphenylsiloxane and dimethylsiloxane end blocked with trimethylsiloxy groups.
To improve the storage stability and reliability of compositions prepared according to the invention, component (A) should contain no more than about 1,000 ppm, preferably no more than about 700 ppm, of any organosiloxane oligomers with less than 20 silicon atoms. Silicone oils most suitable as component (A) having a reduced content of oligomers can be produced by stripping silicone oils with oligomer contents of 10,000-40,000 ppm, after their ordinary equilibrium polymerization. For example, such oligomers can be removed by using thin film evaporators operating at 270-350xc2x0 C. and 0.1-15 mm Hg; by extraction with alcohols such as methanol, ethanol, propanol, and butanol, or with ketones such as acetone and methylethylketone; or by known reprecipitation methods.
Solid silicone resin powder component (B) is used to improve the vibration damping properties of compositions prepared according to the invention. Its content of volatile components must not be more than one percent by weight, preferably not more than 0.7 percent by weight, more preferably not more than 0.5 percent by weight, and even more preferably not more than 0.3 percent by weight. As used herein, the term volatile component refers to low molecular compounds which can be volatilized when heated at 200xc2x0 C. for two hours. In particular, it refers to moisture, alcohols, and low molecular weight siloxane oligomers. For example, when component (B) is a silicone resin powder containing silsesquioxane units in its main skeletal structure, branched siloxanes such as (RSiO3/2)4 and (RSiO3/2)6 represent some of the low molecular weight siloxane oligomers which should be removed. R is defined below.
Silicone resin powder component (B) can be an organopolysiloxane containing RSiO3/2 units and/or SiO4/2 units in the main skeleton structure. Component (B) may also contain R2SiO2/2 units and/or R3SiO1/2 units. An organopolysilsesquioxane powder containing RSiO3/2 units is most preferable. In these unit formulas, R is a monovalent hydrocarbon group among which are alkyl groups such as methyl, ethyl, and propyl; alkenyl groups such as vinyl, allyl, and butenyl; and aryl groups such as phenyl and tolyl. R can also be a halogenated alkyl group such as 3,3,3-trifluoropropyl. In addition, some of these groups may be substituted by hydroxyl groups or alkoxy groups such as methoxy and ethoxy. Alkyl groups are preferred, in particular the methyl group, as such compositions possess a low degree of change in viscosity in response to temperature, and have excellent storage stability.
While R may be the same or different, at least 50 percent of the R groups are preferably methyl groups. While a small number of hydroxyl groups or alkoxy groups such as methoxy and ethoxy can be present at terminal ends in the molecular chain of the silicone resin powder, it is preferred that the number of such groups be very low as such groups generate volatile components, and it is necessary to the amount of volatile components to less than one percent by weight. Component (B) should have an average particle size of 0.1-100 xcexcm, preferably 10-40 xcexcm. The shape of the particles can spherical, oblate, or irregular.
The silicone resin powder component (B) can be produced by hydrolytically condensing chlorosilane or alkoxysilanes corresponding to the RSiO3/2 units, SiO4/2 units, R2SiO2/2 units, or R3SiO1/2 units, followed by washing, drying, and grading. For example, according to one process, a filtrate is obtained by placing methyltrichlorosilane in water, subjecting the filtrate to hydrolysis, and then washing and neutralizing the solution and carrying out filtration. It is then dried by heating and graded. The temperature used during the drying process is preferably 150-300xc2x0 C., more preferably 200-300xc2x0 C., and even more preferably 240-300xc2x0 C. When the heating temperature is less than 150xc2x0 C., the content of volatile components may exceed one percent by weight, and when it exceeds 300xc2x0 C., oxidative degradation of the silicone resin powder may occur. Should the content of volatile components exceeds one percent by weight, solvent extraction and refining by re-precipitation can be used in conjunction with the adjustment in heating temperature.
The hygroscopicity, i.e., the weight increase ratio, of silicone resin powder component (B) is preferably not more than one percent, more preferably not more than 0.6 percent, as determined by maintaining it at a temperature of 25xc2x0 C. and humidity of 95 percent for four hours. The amount of component (B) to be added per 100 parts by weight of component (A) can be in the range of 10-300 parts by weight, preferably 10-150 parts by weight. When the amount of component (B) is less than 10 parts by weight, the vibration damping properties of the composition of the invention tend to deteriorate, and when it exceeds 300 parts by weight, its operating properties deteriorate.
In addition to components (A) and (B), compositions according to the invention can include other components, among which are inorganic micropowders such as glass micropowder, silica micropowder, clay, bentonite, diatomaceous earth, and quartz powder; organic resin micropowders such as acrylic resin micropowder, fluororesin micropowder, and phenolic resin micropowder; anti-oxidants; rust preventatives; flame retardants; pigments; and dyes. The composition can be used in the form of a viscous liquid or semi-solid state at room temperature.
Compositions containing components (A) and (B) can be prepared by combining the ingredients and kneading them with a ball mill, a vibrating mill, a kneader-mixer, a screw extruder, a paddle mixer, a ribbon mixer, a Banbury mixer, a Ross mixer, a Henschel mixer, a flow jet mixer, a Hubbard mixer, or a roll mixer. Heating may be used during the mixing process, preferably at a temperature of 30-200xc2x0 C. While the pressure used during mixing may be atmospheric, mixing under a reduced pressure is preferred.
The composition of the present invention has superior vibration damping properties, and its properties are little influenced by temperature fluctuations. Since it contains a silicone resin powder with a reduced content of volatile components, in comparison to other silicone resin powders, it has excellent long term storage stability. Because of these advantages, the composition can be used in shock absorbers prepared by filling elastic containers such as rubber bags or rubber cylinders with the composition. It is particularly suitable in shock absorbers used in electrical and electronic equipment in environments where there exist considerable temperature fluctuation, such as in compact disk players, compact disk changers, mini-disk players, and car navigation devices.